Carpal tunnel syndrome is a debilitating condition which afflicts many people. It is commonly associated with activities involving repetitive movements of the wrist and hand, and is therefore prevalent in the workforce. Associated conditions include diabetes and hypothyroidism. Conservative measures of rest, immobilization and anti-inflammatory medication are effective alternatives to surgery in approximately 50% of cases.
The syndrome is a compression neuropathy where the median nerve is compressed in the carpal tunnel. Traditionally an open surgical release of the transverse carpal ligament to decompress the median nerve has been the treatment of choice. However, this technique requires a large incision beginning one centimeter proximal to the volar wrist flexion crease, extending 5 to 6 centimeters (cm) distally. The incision is carried through the skin, subcutaneous fat, and palmar fascia in order to expose the ligament. While this technique permits constant visualization and control, it is followed by significant postoperative pain, scarring, loss of grip and pinch strength. Typical recovery time is usually 8-12 weeks.
In an effort to minimize trauma to surrounding tissue, surgeons have developed procedures for cutting the transverse carpal ligament through a small transverse entry portal near the patient's wrist utilizing endoscepic techniques.
One such technique, described by Agee et al., involves insertion of a blade assembly through a small wrist incision. "The Agee Surgical Technique and User's Guide", 3M HealthCare (1990). The assembly includes a blade which is distally located from a viewing port. Thus, with the Agee device, the surgeon cannot actually view the ligament cutting procedure. Consequently, accidents such as severance of the median nerve have occurred. Another problem with Agee's technique is that the entire cannula/blade assembly must be repeatedly moved during the procedure, thereby increasing the probability of injury to surrounding tissue or structures.
Another endoscopic technique, discussed by C. Y. Chow in "Endoscopic Release of the Carpal Ligament: A New Technique for Carpal Tunnel Syndrome", The Journal of Arthroscopic and Related Surgery, Vol. 5(1), pages 19-24 (1989), requires two incisions located on opposite sides of the transverse carpal ligament. The surgeon cuts an entry portal near the patient's wrist and an exit portal in the patient's palm. An open ended cannula is passed into the wrist portal, under the transverse carpal ligament and out the palm portal. The surgeon inserts a knife through one end of the cannula and an endoscope through the other end of the cannula. A problem with this technique is that it requires two incisions rather than one. Another problem is that the palm incision must be performed quite precisely in order to avoid severing palmar nerves and arteries. An additional problem with Chow's technique is that cutting is performed from proximal to distal edges of the ligament putting distal structures such as nerves and arteries in jeopardy.
Another endoscopic technique, disclosed by Okutsu, et al. in "Endoscopic Management of Carpal Tunnel Syndrome", The Journal of Arthroscopic and Related Surgery, Vol. 5(1), pages 11-18 (1989), involves inserting a clear plastic endoscopic sheath into a wrist incision. A hook knife is eventually used to cut the ligament while the procedure is viewed through the transparent sheath. A problem with this approach is that there is no sheath for the knife to prevent accidental cutting while moving the knife to and from the intended cutting position.